Standards are set by national or international bodies, which ensure ‘compliance with a set of design rules by a large community’. (Dix et al. 1998:191) An example is the International Organization for Standardization’s ‘Software ergonomics for multimedia user interfaces’. (ISO 2002:3) ‘Incompleteness of theories underlying the design of interactive software makes it difficult to produce authoritative and specific standards’. Hence, most of the design rules for interaction design are in the form of general guidelines. These guidelines can be applied at various stages of the design. Generally, the more abstract the guideline, the more suitable it is in informing the earlier stages of design such as the requirements specification. More specific guidelines are most appropriate for detailed design. An example of a set of guidelines is the ‘Apple Human Interface Guidelines’. (Apple.com 2003:1)
These guidelines and rules have been formulated from design principles which are a derivative of ‘theory-based knowledge, experience, and common sense’. (Preece et al. 2002:21) One important example is consistency, a principle that is concerned with ‘designing interfaces to have similar operations and use similar elements for achieving similar tasks’. (ibid. 2002:24) Internal consistency relates to uniformity within the design. An example of this is that buttons such as ‘help’ and ‘back’ are the same for all pages. External consistency can be achieved by the similarity of execution of tasks between the interface and the physical world. A map is a good example of this, where the user gradually hones in on a specific destination. Another form of external consistency is the use of similar terminology and functional attributes across platforms or commonly used interfaces. An example here is a ‘back’ button and the Windows ‘minimise’, ‘maximise’ and ‘close’ buttons which are utilised in popularly used interfaces such as ‘Internet Explorer’. (ibid. 2002:24, 25)
